CHAPTER-2 Application of Video Spectral Comparator...

CHAPTER-2

Application of Video Spectral Comparator

for Examination of Printed Material

Application of Video Spectral Comparator for Examination of Printed Material Page 17

2.1 Introduction

Historically the document examiner mainly examined handwritten and typed documents. With

the evolution in technology the typewriter has almost been replaced by the printers of one sort or

another. Spurious documents which relate to one’s identity are often produced to support an

application for passport, driver’s license, bank account or loan, or birth certificate. Sometimes

there is a need to identify whether the suspected printer was used to print the fake document or

not. Usually the question is whether or not a specific printer or photocopier has produced a

particular document. Various printers provide different and valuable evidence based on ink

characteristics and individual printer defects which leave some specific wear and tear marks on

the paper in the form of striations etc. The various chemical and physical examination can reveal

the differences between the printed documents taken from two different printers.

Document examination supports the non destructive examination of document so that the

document remains intact. Video spectral comparator is one of the versatile instruments which

allows non destructive examination of document using multiple instrumental parameters and

provides instant results with easier use. The video spectral comparator is an imaging device

which allows an examiner to analyze inks, visualize hidden security features, and reveal

alterations on a document. VSC works on the basic principles of light. Light is a form of

electromagnetic radiation. The visible region is in the range of 400 nm-700 nm in the

electromagnetic spectrum. When the eye sees different colours, it actually perceives different

wavelengths of light. When light directed towards an object any of the one of five things usually

occurs depending on the emitted wavelengths and the composition of the object:

Reflection:-whole of the light or a part of it can be reflected off the object making it

appear white (if white light is emitted) or lighter (if only specific wavelengths are

emitted).

Absorption:- All or most of the light can be absorbed by the object. The object then

appears black or darker.

Reflection and Absorption:- A part of the light can be reflected, and part can be

absorbed. It produces colours in the visible portion of the spectrum.


Transmission:-Light can be transmitted through the object.

Luminescence:- Light can strike the object, be absorbed, and then reemitted at a longer

wavelength. The phenomenon is known as luminescence.

Infrared (IR) and ultraviolet (UV) radiations are not visible to the human eye. However, all five

mentioned effects that occur in the visible portion of the spectrum also occur in the IR and UV

portions. There can be an important difference. The same object that absorbed light in the visible

spectrum and appeared black, can now transmit radiant energy in the IR spectrum and appear

clear like a piece of glass. For instance, the VSC5000 camera operating in the IR portion of the

spectrum can capture an image lying underneath an opaque blue ink, similar to the way an X-ray

captures images of bones through skin.

Principle of VSC

The VSC5000 consist of two components a desktop computer that runs on software and an

imaging device that include7s a colour charge coupled device (CCD) video camera, a black and

white CCD video camera, excitation/barrier filters, and various radiant energy sources (tungsten,

halogen, and fluorescent lamps). The instrument is equipped with the specialized lighting tools

for examination of documents. The visible, infrared, infrared luminescence, ultraviolet,

transmitted, coaxial and the oblique lighting conditions may be used alone or in combination.

The VSC5000 includes an automated spectrometer that uses the video camera and camera

bandpass filter to analyze the light originating from some region of interest (ROI) in the

document. VSC consist of a variety of illumination and filtering devices to reveal differences in

IR absorption, transmittance, and luminescence and long wave UV excitation of visible

luminescence (Fluorescence) of ink. By selecting different Illumination Modes, features hidden

to the naked eye can be revealed.

The instrument allows viewing and recording the response of documents/inks on exposure of

light of various wavelengths. This is useful for the examination and comparison of inks, the

examination of security features in documents such as passports and driving licenses, the

examination of altered or obliterated entries and the examination of entries which have faded or


been washed out. It permits the analysis and comparison of inks revealing alterations on a

document. It visualizes security features printed into papers and allows a quick examination of

the entire questioned document.

Figure-2.1 The VSC-5000 Equipment

The analysis may reveal ink differences in context, or similarities in chemical formulation. The

graphical user interface allows examiners to control the VSC-5000 more easily. Spectral analysis

is performed over the Wavelength band 400 – 1000 nm. comparisons can be made between

images side by side on a split screen, overlaid or with strobe display with an image rotation

feature for alignment.VSC facilitate colour measurement and chromaticity display charts and a

high resolution grating spectrometer for recording absorption, reflectance, transmission and

fluorescence spectra.

Printing examination using Video Spectral Comparator

The VSC-5000 can be used to examine printed documents. The examination under different

lighting conditions can show that a document has been altered. If an additional paragraph or line

has afterward been added to a document or a page is replaced with containing different

information. Even without the source printer, it may be possible to opine that two documents

were both produced using the same printer or not. Counterfeit pharmaceuticals, cigarettes,


security documents etc can be examined by looking at the packaging. By comparison of with

genuine packaging it is possible to link counterfeit packaging together by printing methods and

defects. If the printers which have been used to produce the packaging are found then it is

possible to link the counterfeits to the printers.

Josey et al., (2000), reported comparisons of different models of the Foster & Freeman Video

Spectral Comparator (VSC) equipment. The study discriminate matched pairs of black and blue

liquid (water-based) and non-liquid writing inks by microscopy, VSC, Laser, and UV-IR-VIS

spectroscopy. The VSC examinations were performed as monitor-assessed video spectral

comparisons of IR, Infra Red Luminescence, and UV fluorescence responses of the inks. Liquid

ink included roller-ball and fiber-tip; non-liquid included ballpoint. They concluded that VSC-1,

successfully discriminated 79.50% of the pairs while the newer VSC-2000 correctly

discriminated 95.80%. Of all the inks the older model did not discriminate, some were actually

distinguishable by microscopic examination.

2.2 Experimental

2.2.1 VSC Instrumentation

The Windows™ based software version 5.7embedded in VSC 5000 from Foster + Freeman was

utilized in the work.

VSC-5000 provides the illumination by spot lamp, Flood light, UV-365, 312, 254, transmitted

lights, coaxial light, anti-stokes and light from right & left side. In this study flood light was used

which illuminate the sample from above. A flood light is an artificial light providing even

illumination across a wide area.

Table-2.1 The optical conditions of instrument used in study

Process Lamp Type

Spectrum Wavelength (nm) Illumination

Incandescent Filament Lamp Filament Bulb Visible/IR 400 -1000 Flood


2.2.2 Scheme for Sample Collection

The sample documents were collected in the form of printed documents from 32 inkjet printers.

Each printout was containing four rectangular blocks of Cyan (aqua), Magenta, Yellow and

Black colour. The colours were prepared by keeping the constant value of Red, Blue & Green in

the colour palette of MS-Office (Nicholas 2003). Table 2.2 shows the values of Red, Green and

Blue to create Cyan, Magenta, Yellow and Black colour. The RGB scheme used was as follows:-

Table-2.2 Values of RGB (Red, Green, Blue) in colour palette of MS-Word application of

Windows used for printing of documents on the same substrate of paper ‘Bilt copier’.

Paper used to print samples

White paper of A4 size from ‘Bilt Copier’ company manufactured in 2008 by ‘Ballarpur

Industries Limited’ GSM 75 was used throughout the study to take print sample.

2.2.3 Sample Preparation

The list of printers used to print the sample documents are listed in Table 2.3 were collected from

different markets of Hyderabad, New Delhi, Agra and Allahabad. During random sample

collection majority of HP printers were encountered.

Inkjet Ink R G B

Cyan 0 255 255

Magenta 255 0 255

Yellow 255 255 0

Black 0 0 0


Table-2.3 List of printers used to print the sample documents along with Brands & Models

of Inkjet Printer

S.No. Sample No. Model

Brand- HP

1. 1 HP DeskJet 1050 J410 (M-1)

2. 2 HP DeskJet 1050 J410 (M-2)

3. 3 HP DeskJet 1050 J410 (M-3)

4. 4 HP DeskJet F4185

5. 5 HP PSC 1608

6. 6 HP DeskJet D1550

7. 7 HP DeskJet 5550

8. 31 HP Photosmart D7168


10. 10 HP Photosmart C4688

11. 26 HP DeskJet D1668 (M-1)

12. 27 HP DeskJet D1668 (M-2)

13. 28 HP Officejet 4355


15. 8 HP Business Inkjet 1000 (M-1)



Brand- Canon

18. 12 Canon Pixma MP-258

19. 13 Canon Pixma IP 2770

20. 20 Canon Pixma MX308

21. 21 Canon Pixma ip 1300

Brand- Epson

22. 14 Epson Stylus TX121

23. 15 Epson R-220

24. 17 Epson Stylus Photo R230X

25. 22 Epson Stylus T13 (M-1)

26. 25 Epson Stylus T13 (M-2)

Brand-Brother

27. 16 Brother MFC-295 CN

28. 18 Brother MFC-J415 W

29. 19 Brother DCP J125 (M-1)



32. 29 Brother DCP 6690 CW


2.2.4 Sample Pool

32 coloured printouts were taken from different Inkjet printers. The Cyan, Magenta, Yellow and

Black ink, the four major colour components were the target ink.

The all coloured ink samples were then marked as the sample identification no. 1-C,2-C,3-C,4-C

……32-C for Cyan colour ink, 1-M,2-M,3-M,4-M ……32-M for Magenta colour Ink, 1-Y,2-

Y,3-Y,4-Y ……32-Y for Yellow Colour Ink and 1-K,2-K,3-K,4-K ……32-K for Black colour

Ink.

32 samples of each Cyan, Magenta, Yellow & Black Colour i.e. Total number of samples 32X4=

128 were analysed.

2.2.5 Analysis

The sample to be examined was placed on the document platen under the canopy (Manual,

VSC-5000). The document was viewed by a video camera and a live image was shown on the

monitor. The document was then illuminated under flood light and the reflectance spectra were

then recorded after selecting the position of the region of interest of the sample and standard

white. A region of interest (ROI) was specified on the document from which the light is collected

for analysis.

The same procedure was then followed for recording spectra for all samples of four target inks.

The images of sample document were documented by taking the images in normal flood light

without any magnification.

2.2.6 Documentation

The images of sample document were documented by taking the images in normal flood light

without any magnification.

2.2.7 Consistency

The reproducibility of the results for the same samples was checked 5 times by repeating the

same experiments for five continuous days.


2.3 Result and Discussion

Usually document examiners are asked to examine printed documents and to fix their source of

origin. Usually when the questioned document is a counterfeit currency, cheque, stamp papers

etc or where, there is a small amount of document is present and where there court does not

permit for the destructive examination then there is a need arrives for the technique which allows

a non destructive examination of document. In order to overcome from this problem a spectral

examination was conducted. The VSC5000 includes an automated Spectrometer that uses the

Video Camera and Camera Bandpass Filter to analyze the light originating from some Region of

Interest (ROI) in the document. Spectral analysis is performed over the Wavelength band 400 –

1000 nm (Manual VSC 5000, 2005).128 samples, 32 each for Cyan, Magenta, Yellow and

Black were analyzed using VSC and the spectra were presented. Figure 2.2-2.12 shows the

graphs of all of the inks plotted as light intensity (expressed as a % of maximum) against

wavelength over the range of 400 nm to 1000 nm. Figure 2.2 shows the comparative spectra of

Yellow colour for HP brands. During the study it was found that Yellow colour inks are not easy

to differentiate as all of the inks samples were showing the almost similar percentage of

maximum intensity at same wavelength as shown in Figure 2.2-2.4.Figure 2.3 shows the

variation in sample no. 17 and 20 which are showing intensity at about 80% while the intensity

of rest of the samples are almost equal around 90-100%. A little variation in sample no.25 is

shown in Figure 2.4.

Figure 2.2: Comparative VSC spectra for Yellow colour of HP brands for sample number

1-4, 6-11.

100-110%

90-110%


Figure 2.3: Comparative VSC spectra for Yellow ink of sample no. 13-22.

Figure 2.4: Comparative spectra of Yellow coloured ink for sample no. 23-28, 31-32.

A little but significant variation was observed in the VSC spectra of Cyan and Magenta coloured

ink as shown in Figure 2.5-2.7.

From the Figure 2.8 the distinct spectra of sample number 10 and 11 can be observed for various

Magenta coloured ink samples.

Approx 80%

90-100%


Figure 2.5: Comparative VSC spectra for Cyan ink for sample no.1-4,6-12.

Figure 2.6: Spectra for Cyan colour for sample number 12-22.


Figure 2.7: Spectra of Cyan colour for sample number 23-29, 31-32.

Figure 2.8: Spectra for Magenta ink for sample no.1-4, 6-12.


Figure 2.9: The comparative spectra of Magenta coloured ink for sample no.22-29.

More significant variation was observed in the different sample of Black coloured ink. The ink

samples of Black colour are showing absorbance at high wavelength, it may be due to the reason

that the Black colour is a combination of several colours (Henry, 1917). As a trail TLC of black

ink was carried out and it was found that black ink is a combination of several coloured inks.

Figure 2.10: Comparative VSC spectra for Black coloured ink of all four brands sample

no 1-4, 6, 8, 10-12.

20%-30%

20%

100%


Figure 2.11: Comparative VSC spectra for Black colour of all four brands for sample

number 13-22.

Figure 2.12: Comparative Spectra of Black colour for sample number 23-29, 31, 32.

The variation in sample 2 in Figure 2.10 and in samples of Figure 2.11 and Figure 2.12 can be

observed.

90%-100%

25%-40%

90%-110%

20%-30%


2.4 Conclusion

The VSC scan in the visible and partial NIR range (400-1000nm) for various coloured inks

(yellow, cyan, magenta) and black ink indicates characteristic absorption patterns. Among the

same print colour inks of different manufacturer variations were observed which may be taken

into account for forensic comparison. It was observed that the inter manufacturer difference were

more in the magenta colour and maximum in black colour. In day to day document examination

black printer inks are commonly encountered and hence the proposed methodology can be used

successfully with confidence to differentiate between the black coloured cartridges of different

manufacturers through their characteristic absorption spectra. The reasons for this are obvious as

the black ink is a mixture of several colours and each manufacturer may be mixing different and

specific colours in varying proportions. This variation can be used for the forensic comparison of

the printed documents. In conclusion the proposed VSC technique can be used for the

comparison of the printed documents. In conclusion the proposed VSC technique can be used for

the comparison of various coloured print inks in general and more particularly the black inks.

The technique is more suitable when the specimen comparison material is available.

CHAPTER-2 Application of Video Spectral Comparator...

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